The present invention relates generally to motor driven reversible actuator mechanisms, and more particularly to mechanisms that allow the manual setting of the position of motor driven reversible actuator mechanisms.
Motor driven actuator mechanisms for use in controlling the position of valves, dampers, etc. typically include a motor that drives an output coupling in one direction through a gear train to position the valve, damper, etc. in a desired position. Spring type or fail safe actuator mechanisms also typically include a torsion spring coupled to the gear train that is wound during energization of the motor. In this way, energy for rotating the shaft in the other direction when the motor is de-energized is stored in the spring. Upon loss of power to the motor, the torsion spring unwinds, driving the gear train to position the valve, damper, etc. in a desired or fail safe position. Such actuator mechanisms are described in U.S. Pat. No. 5,310,021, entitled Motor-Driven, Spring-Returned Rotary Actuator and U.S. Pat. No. 4,595,081 entitled Reversible Rotary Actuator With Spring Return, both of which are assigned to the assignee of the instant application, the teachings and disclosures of which are incorporated in their entireties herein by reference thereto.
In such rotary actuators the motor rotates the output shaft and winds the spring by way of a gear train which substantially reduces the speed and substantially amplifies the torque of the motor. When the spring unwinds to rotate the output shaft, the spring acts reversely through the gear train and backdrives the motor shaft. An actuator of this type is frequently used to drive a utilization device such as a damper in the duct of a heating, ventilating and cooling system. When the motor is de-energized, the spring drives the output shaft in a direction moving the damper to a closed position against a fixed stop. The effectiveness of the seal of the damper against this fixed stop is somewhat a function of the amount of spring force remaining in the torsion spring when the damper encounters the stop. If this position is reached when the spring has released all of its stored energy, the quality of the seal against the stop is determined solely on the quiescent mechanical contact between these two surfaces, taking into account the mechanical connection to the motor through the gear train.
While such contact between the damper and the fixed stop may be adequate to stop flow through the damper for many installations, certain installations may require that the seal between the damper and the stop be positively held. That is, there are some installations that require that the damper be able to remain positively closed with increased pressure. Such positive closing force against the fixed stop is particularly desirable in higher pressure installations and in valve operations. Indeed, nearly all installations could benefit from such a positive closing force imparted by the spring to ensure the integrity of the closed position.
To provide such a positive closing force on the damper, valve, etc. driven by the spring return actuator, the output coupling of the actuator is often rotated a few degrees before being connected to the drive shaft of the driven device (e.g., damper, valve, etc.). Such rotation of the output coupling winds the spring to establish a preload. Once a spring preload is established, the output coupling of the actuator is connected to the drive shaft of the driven device that is positioned in its closed or failsafe position (referred to herein as the zero position). Once connected, the spring impart the positive preload force on the driven device at its zero position.
Unfortunately, since the output coupling of the actuator is coupled through a torque multiplying gear train, rotation of this output coupling by hand is somewhat difficult. Further, since the return spring also acts through the torque multiplying gear train, holding the output coupling at the preload position while trying to connect this output coupling to the drive shaft of the driven device is also quite difficult.
In view of the above, the present invention is directed to a new and improved spring return rotary actuator that includes a manual override that allows the imparting of a preload on the return spring in a simple and effective manner. Further, the invention is directed to a new and improved spring return rotary actuator having such a manual override that includes a locking mechanism capable of locking the output coupling from rotating under influence of the return spring.
A rotary actuator in accordance with one embodiment of the present invention comprises a motor, a gear train, and an output coupling driven by the motor through the gear train. The gear train multiplies the torque of the motor to drive the output coupling. A manual override mechanism having a user accessible interface is also included. The manual override mechanism operates in conjunction with the gear train to allow manual positioning of the output coupling. Further, a manual locking mechanism having a user accessible interface is also included. This manual locking mechanism engages the gear train to prevent rotation of the output coupling in a first direction.
Preferably, the actuator further comprises a spring return mechanism including a torsion spring coupled to the gear train. This torsion spring is wound upon energization of the motor driving the output coupling in a second direction and is unwound upon de-energization of the motor to drive the output coupling through a portion of the drive train in the first direction. The manual override mechanism is coupled through the torsion spring such that operation of the manual override to effect a rotation of the output coupling in the second direction winds the torsion spring. In a preferred embodiment the manual locking mechanism includes a segment gear head having a toothed portion and a smooth portion on its face. The segment gear head is rotatable between a locked position wherein the toothed portion engages the gear train preventing rotation of the output coupling in the first direction, and an unlocked position wherein the smooth portion is positioned in association with the gear train and the toothed portion is disengaged from the gear train.
Further, the manual locking mechanism preferably includes a reset lock spring operatively coupled to the segment gear head to bias the segment gear head to the unlocked position. The segment gear head also includes a slot adapted to accommodate a stop pin. This stop pin abuts against a first end of the slot in the unlocked position and against a second end of the slot in the locked position. Rotation at a point of engagement with the locking mechanism of the gear train under influence of the torsion spring is in a direction to rotate the segment gear head against the reset lock spring force. This maintains the manual locking mechanism in the locked position. Rotation at a point of engagement with the locking mechanism of the gear train under influence of the motor is in a direction to rotate the segment gear head in accord with the reset lock spring force. This aids the manual locking mechanism to achieve the unlocked position. Preferably, the motor drives the output coupling in a second direction to disengage the locking mechanism from the gear train to allow rotation of the output coupling in the first direction.
In an alternate embodiment of the present invention, a locking mechanism for a motor driven rotary actuator having a gear train drivably coupling a motor to an output coupling to drive a device is provided. This locking mechanism comprises a segment gear head having a toothed portion and a smooth portion on its face. The toothed portion is configured to engage a gear in the gear train. The segment gear head is positioned in relation to the gear such that rotation of the segment gear head between a locked position and an unlocked position results in engagement of the toothed portion with the gear in the locked position and disengagement of the toothed portion in the unlocked position. The segment gear head further includes a slot adapted to accommodate a stop pin, and is positioned in the segment gear head such that the stop pin abuts against a first end of the slot in the unlocked position and against a second end of the slot in the locked position. A reset lock spring is operably coupled to the segment gear head to bias the segment gear head to the unlocked position. Further, a user interface is coupled to the segment gear head to rotate the segment gear head between the locked and the unlocked positions.
In a preferred embodiment the toothed portion of the segment gear head occupies approximately 25xc2x0. Further, the toothed portion is preferably positioned in relation to the slot such that rotation of the gear train at a point of engagement with the locking mechanism is in a direction to rotate the segment gear head such that the stop pin engages the second end. Additionally, the reset lock spring preferably is positioned such that engagement of the toothed portion of the segment gear head with the gear train when the actuator is driving the device to a closed position results in rotation of the segment gear head against the bias applied by the reset lock spring.
In yet a further alternate embodiment of the present invention, a spring return, motor driven rotary actuator for driving a flow control device to an open position under power and to a closed position upon loss of power is presented. This actuator comprises a motor, a speed reducing, torque multiplying gear train drivingly coupled to an output of the motor, and an output coupling drivingly coupled to the gear train. This output coupling is driven in a first direction by the motor. A spring return mechanism including a torsion spring coupled to the gear train is also included. The torsion spring is wound upon energization of the motor driving the output coupling in the first direction, and unwinds upon motor de-energization to drive the output coupling through the drive train in a second direction. A manual override mechanism having a first user accessible interface is provided that operates in conjunction with the spring return mechanism to allow manual positioning of the output coupling and winding of the torsion spring. Finally, a manual locking mechanism having a second user accessible interface is also provided. This manual locking mechanism engages the gear train to prevent rotation of the output coupling in the second direction.
In one embodiment the manual locking mechanism includes a segment gear head having a toothed portion on its face, and is rotatable between a locked position wherein the toothed portion engages the gear train preventing rotation of the output coupling in the second direction, and an unlocked position wherein the toothed portion is disengaged from the gear train. The manual locking mechanism further includes a reset lock spring operatively coupled to the segment gear head to bias the segment gear head to the unlocked position. Additionally, the segment gear head includes a slot adapted to accommodate a stop pin, which abuts against a first end of the slot in the locked position to prevent further rotation of the segment gear head. Further, rotation of the gear train at a point of engagement with the locking mechanism under influence of the torsion spring is in a direction to rotate the segment gear head against the reset lock spring force thereby maintaining the manual locking mechanism in the locked position. Rotation of the gear train at a point of engagement with the locking mechanism under influence of the motor is in a direction to rotate the segment gear head in accord with the reset lock spring force thereby aiding the manual locking mechanism to achieve the unlocked position. Preferably, the motor kicks the output coupling in the first direction to disengage the locking mechanism from the gear train to allow rotation of the output coupling in the second direction.
Other features and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.